Thanks to all who replied - however, none of the routines mentioned do what
I'm looking for. Olin seems to have the clearest picture of what I want. The
software usec delay routine should handle a call from somewhere else in the
program, loop as necessary then return. The time consumed should account for
the call, the overhead, the looping, and the return. Thus, it should look
like this:
        SoftUsecDelay(57);      // C code call

#asm
_SoftUsecDelay:
        overhead
        loop
        return
#endasm

I want to be able to request delays anywhere from 14 to 250 usec and have
the subroutine handle it automatically. Smaller delays can be handled
easily.

I've been going around and around with different ideas for the past few
days, but it seems like I can never be accurate across the scale. I was
hoping that someone had already run in to this before and had come up with a
solution. With all the talent out there, I'm sure someone has and I look
forward to hearing from them. Again, thanks to all who have responded so
far.



-----Original Message-----
From: Olin Lathrop [mailto:olin_piclist@COGNIVIS.COM]
Sent: Thursday, September 07, 2000 12:59 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: usec delay routine


> Does anyone have a simple, yet accurate software usec delay routine?
> I'm running 4mhz PIC16F877 and want to be able to generate a call to
> SoftUsecDelay(NumberOfMicrosecondsToDelay).

For short delays you can just jump into a list of NOP instructions.  If you
wanted to make a fancy routine, it would first subtract off all its own
overhead, then use a loop for multiples of the loop time, then jump into a
list of NOPs for the exact remainder.  Of course interrupts would need to be
off for any of this to be valid.

What time ranges do you want to delay for?


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@cognivis.com, http://www.cognivis.com

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